Narrator (April Hobart, CXC): Ultraluminous X-ray Sources, or ULXs, are unusual objects. They are rare and, as their name implies, give off enormous amounts of X-rays. Until now, astronomers thought that ULXs were powered by a system where a stellar mass black hole was in orbit around a neutron star or black hole. However, a study using data from NASA's NuSTAR and Chandra X-ray Observatory shows that this class of objects is more diverse than that. With NuSTAR, astronomers discovered regular variations, or pulsations, coming from a small region in the center of the galaxy M82, which is located about 11.4 million light years from Earth. The researchers then used Chandra, with its exceptionally keen vision in X-ray light, to pinpoint exactly which source was giving off these pulsations. This source is called M82X-2. It's hard to explain how a system with a black hole could generate the pulsations seen by NuSTAR. Because of this and other data, astronomers think that M82X-2 is the brightest pulsar ever seen. Pulsars are rapidly spinning neutron stars that sweep beams of radiation out like a lighthouse, and this is what would explain the pulsations of X-ray light seen in M82X-2. ULXs just became a little more unusual and intriguing to study.